The popular silver fronted Hi-Fi units that were seen on the market from the
big Japanese manufacturers doing the late 1960s and through the 1970s led
to an interesting phenomenon. Most of the units produced were aimed at the
lower end of the market, which is where the profits were in mass production.
Each maker had top of the range products aimed at the real Hi-Fi enthusiast or at the more well heeled buyer. Hence some very high quality 'no expense spared' amplifiers and receivers were made available. While the more budget priced ranges might offer output powers of from 15 to 30 Watts per channel, the top end models offered from 75 to 300 Watts per channel with a very versatile range of inputs, tone controls and even phono cartridge equalisation.
They were designed to suit a wide range of ancillary equipment like tape decks, tuners and turntables. Marantz was considered one of the premier brands, but all of the main manufacturers, Luxman, Pioneer, Sansui, Sony, Nikko, JVC and Onyo had their flagship models that were built to a very high standard, some even better than the very collectable Marantz range.
These amplifiers and receivers were originally built using all discrete components meaning that separate transistors were used throughout. Only later in the 1970s did integrated circuits start to be used, which to Hi-Fi enthusiasts and audiophiles was a retrograde step as sound quality was thought to suffer from the use of these new components. By the early 1980s the Hi-Fi makers were moving away from the silver fronted designs and producing black faced equipment in pressed steel cabinets.
The 1960s and 70s had seen a predominance of wood veneer cabinets, even on
relatively inexpensive models. With the dark facias came what is perceived
to be a degradation of sound with ever more integrated circuits being used
to keep manufacturing costs down. Some audiophiles refer to this and subsequent
decades as 'the Dark Ages' of Japanese Hi-Fi.
Due to ageing of components, especially electrolytic capacitors, even what appears to be a fully working amplifier or receiver can benefit from a general overhaul. This would include the replacement all electrolytic capacitors, some other capacitors in critical areas such as coupling and any resistors that have strayed from their original value. This will generally bring about a marked improvement in sound quality, especially if good quality components intended for audio are used.
Replacing damaged transistors in equipment built 40+ years ago can be a little more tricky. The specific type is likely to have gone out of manufacture many years ago, so reliance on 'new old stock (NOS) components or near equivalents is normal. Some power output transistors are now very rare and consequently expensive. This has lead to some unscrupulous suppliers relabelling transistors and passing them off as new new old stock. These usually differ considerably in specification and performance from the original. A search on the internet may show up many suppliers of a certain type of old transistor, usually in China. On close examination and testing these are relabelled devices of much more recent manufacture. Finding reliable replacements can be very time consuming and consequently expensive!